Field of the Invention
The present invention relates to material handling pallets, and in particular to a plastic pallet having superior longevity compared to existing wood and prior art plastic pallets.
Description of the Prior Art
Pallets of all description are in one way or another involved in the supply chains and logistic channels that deliver the vast majority of all products that are relied upon by society to exist. Wood pallets of many dimensions have been used in North America since after WWII due to the abundance and low cost of wood. The largest user groups of wood pallets over time have established standard pallet dimensions for each of their respective industry logistic networks. The largest user group of pallets in North America established a 48×40 inch pallet dimension standard may years ago, so that today most pallet loads delivered to distribution centers and supermarket stores use a 48×40 inch pallet. So many 48×40 inch wood pallets were used by industry that there was an opportunity for a company to create a pool of 48×40 inch wood pallets that could be rented for a uniform nationwide fee structure in sufficient quantity and convenience. Pallet pooling functions as an alternative to buying white wood pallets offered by hundreds if not thousands of pallet manufacturers scattered throughout North America at different prices and quality levels determined by regional market conditions. One such company that capitalized on the opportunity to supply a pooled wood pallet in competition with the independent white wood pallet manufacturers was Brambles, an Australian company, which through its subsidiary CHEP USA became the predominant pallet rental company with +/−100 million 48×40 inch wood pallets for rent in North America.
Wood pallets however fall apart due to wear and tear in use so that wood pallet pooling companies have to charge their customers a significant pallet rental fee that includes the cost of required repeated repair of the wood pallet for continued re-use. It is commonly understood +/−34 percent of the wood pallet rental fee is attributed to wood pallet maintenance. Plastic pallets have been proposed to replace wood pallets. Plastic pallets are understood to be less prone to damage, and despite their original higher cost, have a lower cost in practice than wood pallets. In addition, plastic pallets have a residual value equal to 75 percent of the cost of their virgin plastic material content, so that in ten or more years, the value of the plastic pallet as a recyclable commodity is greater than the original cost of the plastic pallet resin material. The long term operating costs of a wood pallet are therefore higher due to ongoing maintenance costs than the original cost of the long lasting plastic pallet, so that the original lower price advantage of wood is lost to plastic. Thus plastic pallets are expected to gain a greater share of the 48×40 inch wood pallet market in North America.
Many proposed plastic pallet designs and structures measuring 48×40 inches have been offered to replace pooled 48×40 inch wood pallets. However, with the passage of time, it has been discovered that plastic pallets are also prone to wear and tear, presented by the effects of delamination, punctures, cracks and the like. These problems are not presented in wood, so plastic pallets have unique problems only recently realized. The prior art plastic pallets have not fulfilled the promise of a maintenance free pallet. Thus the price advantage of plastic pallets over the long run is lost. Consequently, wood remains the dominant material in the market to this day.
The iGPS pallet rented by iGPS Company, L.L.C. headquartered in Orlando, Fla. is the most widely used pooled plastic pallet in North America. The iGPS pallet is disclosed in U.S. Pat. Nos. D544175, 7,779,763 and 7,841,281 to Valentinsson, which are incorporated herein by reference. The so-called second generation iGPS pallet with vent holes in the upper deck surface is intended to provide a number of advantages to shippers who intend to replace traditional wood pallets with the iGPS pallet. This plastic pallet is supposedly superior to a wood pallet because it allows for tracking technology to be built into the pallet; is lower weight which saves on shipping costs and workplace injuries; is more durable, eliminating inherent wood repair and maintenance; has greater uniformity, reducing customer equipment and product damage; has reduced bacteria, mold and insect infestation; and is less flammable and has superior environmental sustainability.
Although prior art plastic pallets are an improvement over traditional pooled wood pallets, they suffer from many unique problems that are not encountered by pooled wood pallets.
The Valentinsson pallet is constructed from a unique combination of a first twin sheet deck and a second injection molded base. The deck and base are separately manufactured using two different production facilities. The twin sheet deck is constructed from two high density polyethylene (HDPE) plastic sheets that are sequentially thermoformed against first and second mold surfaces and then pressed together under heat, vacuum and pressure between two molds. The unitary construction of the twin sheet deck is resilient and fusion at the mating surfaces is long lasting and essentially permanent. The injection molded base is an assembly that includes a first upper injection molded section and a second lower injection molded section. Five steel reinforcement bars and four RFID tags are positioned between the sections before the upper and lower sections are fused together to form the base in a secondary operation. The deck and base are subsequently fused together in a final assembly operation to produce an operational pallet.
As a pooled returnable asset, each such pallet is intended to survive at least 60-80 trips in a period of 10 years. A comparable pooled wood pallet with extensive repairs and maintenance may enjoy 70 trips in 20 years. However, these plastic pallets are not surviving their intended number of trips and are suffering catastrophic damage in use. A routine inspection of ten randomly picked well-used pallets reveals eight are defective. All of the displayed defects concern the injection molded base and the fusion of the base to the deck. The twin sheet decks display wear and tear but no catastrophic damage is evident. The most frequent defects show separation where the upper and lower injection molded sections of the injection molded base are the fused together around the 48×40 inch perimeter. Such delamination is a catastrophic problem because the interior of the injection molded structure is no longer sealed against penetrating liquids, chemicals, dirt, debris, bacteria, insects and the like. Secondly, the top section of the injection molded base demonstrates cracks which indicate the materials are affected by cold condition impacts. Cracks admit additional materials into the cavities of the pallet which accumulate and add weight and corrode the steel reinforcement bars or deteriorate the performance of the RFID tags placed in the legs of the base of the exemplary pallet structure. A third observation is that the nine leg structures of the injection molded base are delaminating from the deck around the perimeter of the leg receiving pocket structures in the lower sheet section. This lesser problem indicates the difficulty of permanently fusing together two dissimilar plastic materials used to create the Valentinsson pallet. In use the injection molded components of the so-called 2nd gen-pallet suffer catastrophic damage which is difficult and expensive to repair, so that the operating expenses of the exemplary plastic pallet are actually costlier than the operating expenses of wood pallets.
A fourth observed wear and tear problem with all plastic pallets concerns fork lift, pallet jack and pallet moving equipment related pallet damage. In operation a fork lift operator impacts a plastic pallet structure supporting a 14,000-pound load on the ground with pointed fork tines. Because of misjudgement, the wall of the impacted plastic pallet will very likely be punctured or pierced on a direct hit or tear when grazed by the forks. Twin sheet and injection molded leg walls cannot recover from these forces under compression. If the pallet is idle and unloaded in storage, the equivalent inertial impact is typically sustainable because the pallet moves with impact. Therefore, fork impacts under load represent a significant wear and tear problem for any pallet because a fractured or pierced pallet admits liquids and materials into the interior of the pallet, which is unacceptable. A plastic pallet meant to weigh less than 50 pounds (tear weight) weighs 65 pounds in use, because the interior spaces of the pallet have accumulated water within its interior spaces which has frozen as a result of been stored outside. Consequently, the pallet is no longer suitable for future rental trips based upon an original equipment standard or specification.
There are other problems with prior art plastic pallets. For example, the impact damages displayed by the injection molded components of the base are aggravated by the fact that fire retardant additives are mixed with the HDPE resins used to construct the pallet in order to achieve a UL safety rating for flammability. These solid materials weaken the impact strength of the resins. Additionally, some of the materials in the fire retardant additives are restricted by state law and there is a general concern the halogenated and other pallet materials for fire resistance are a health and environment risk.
Prior art teaches a twin sheet pallet structure is demonstrably stronger, suffers less wear and tear and is lower cost than an equivalent injection molded structure using the same measure and type of resin materials. Many prior art plastic pallets are injection molded because despite twin sheet's superior performance in many areas, twin sheet thermoforming has an inherent weakness. Single walled pallet legs are crushed under industry proscribed loads (GMA Spec. 15). Twin sheets pallets must therefore have double walled legs for strength, which can only be formed by depressing the material on the load support surface of the pallet deck into the leg pockets to thereby reinforce the pallet legs. This is a fundamental problem because the leg pockets accumulate liquids and debris and besides the industry standards require a minimum of 85 percent deck coverage, where 100 percent is preferred (GMA Spec. 4).
In a 48×40 inch pallet with nine leg pockets, it is impossible to comply with the requirements of industry using a twin sheet pallet assembly with nine leg pockets. The Valentinsson pallet is innovative because it uses a deck that does not include depending leg structures, so that the advantage of twin sheet thermoforming can be put to use with an injection molded base structure that includes the necessary legs. It should be noted that the legs, blocks and other terms used in connection with the structures of a pallet are interchangeable in meaning. Numerous derivatives exist to describe the same essential structures that extend between the deck and the base to admit the entry of fork tines, pallet jacks and other pallet handling equipment. The required pallet admits pallet jacks, forks and equipment and provides 4-way access.
Another problem is that a typical pooled plastic pallet, intended to last +/− ten years, is not easily modified to accept new tracking technology equipment. For example, Valentinsson describes making a knife cut in a groove in the area of a block to open a window into the interior of the corner leg structures. After opening the window and exchanging the transponder, a foaming compound is used to seal the window protecting the replaced transponder. Another example of this procedure is described in FR patent 2697801 dated May 1994, and incorporated herein by reference. The problem with this approach is that the foaming compound is difficult to remove so it is impractical to replace the second transponder with a third transponder should this become necessary.
These and other problems have created the need for a new and stronger plastic pallet.